In sensors of process measurement technology and analysis, optical measuring methods are being used more and more frequently. In these methods, the amplitude and/or phasing of an optical signal changes when it strikes a measurement object, and the changed signal is detected by an optical sensor. An example of the application of an optical measuring method of this type is the measurement of the oxygen content or oxygen saturation of a liquid or of a substance, wherein, for example, a dye is illuminated by a light signal of a previously determined wavelength, amplitude, and phasing, and the luminescent light reflected from the dye is analyzed. When the oxygen concentration in the dye changes, the fade time of the luminescence and thus the amplitude and phasing of the received optical signal also change. With appropriate calibration, the amplitude and phase of the received optical signal are therefore a measure of the oxygen concentration.
Measuring devices of this type must be suitable for use in many areas, simple in design, and as interference-proof as possible against external and internal influences and side effects. For example, they are used in areas at risk of explosion and therefore must consume the least possible amount of energy and thus be assembled from relatively uncomplicated or simple components. In addition, the economic constraints must also be taken into account by using reliable, mass-produced components that are commercially available at low cost.
For this purpose, the functionalities of different components are frequently bundled into microcontrollers; that is, in addition to a data processing microprocessor, other digital or analog components, peripheral functions, or interfaces are also integrated into a microchip. When additional analog or digital components such as a voltage-supply circuit or a driver circuit are used outside the microcontroller of an optical measuring device, direct interference with certain components may occur; or indirect interference may result from parasitic effects originating from power supply lines. Measurement signals can therefore be inaccurate or their evaluation negatively affected, and the result is that the function of the entire measuring device is impaired.
It is therefore the object of the present invention to provide an optical measuring device which largely avoids direct or indirect interference with electronic components, which can be built easily at low cost, and which makes reliable measurement possible.
This object is achieved by the invention described and claimed herein. Particularly advantageous forms and embodiments of the invention are also described and claimed.